Final answer:
It is false that unknown compounds can be identified based solely on their physical properties, as compounds with similar physical properties may exist and require additional analysis for accurate identification.
Step-by-step explanation:
The statement “Unknown compounds can usually be identified based solely on their physical properties” is false. While it is true that each compound has a specific composition and distinct physical and chemical properties, these properties alone are not always sufficient to uniquely identify a compound. There are many compounds with similar or even identical physical properties that can only be differentiated by their chemical properties or by using instrumental analysis to determine their molecular structure. Therefore, a combination of properties and analytical techniques is often required to accurately identify an unknown compound.